% MATLAB script for Illustrative Problem 6, Chapter 6.
% echo on
clear;
N=52;					
noise_var=0.25;
sigma=sqrt(noise_var);			% standard deviation of the noise
I=floor(rand(1,N)*2)*2-1;   % I is -1 or 1
%I(2:N)=0*I(2:N);
% for channel1:
A=1;
B=[0.1 -0.25 1 -0.25 0.1];
rec_sig1=filter(B,A,I);    		% the received signal without noise for channel 1
%rec_sig1=rec_sig1([3:N]);  		% to compensate for the delay in filtering
for i=1:N,
   noise(i)=gngauss(sigma);
end;
% echo on ;
y1=rec_sig1+noise;	   		% received signal with noise for channel 1
% for channel 2:
A=1;
B=[-0.2 0.5 1 0.5 -0.2];
rec_sig2=filter(B,A,I);    		% the received signal without noise for channel 2
%rec_sig2=rec_sig2(3:N);	   		% to compensate for the delay in filtering 
for i=1:N,
   noise(i)=gngauss(sigma);
   % echo off ;
end;
% echo on ;
y2=rec_sig2+noise;         		% received signal with noise for channel 2
% plotting commands follow
figure,
stem(3:N+2,I),title('藍(lán)色：原始信號(hào)；綠色：ISI；紅色：ISI+noise')
hold on
stem(1:N,y1,':r')
stem(1:N,rec_sig1,':g')
hold off
figure,
stem(3:N+2,I),title('藍(lán)色：原始信號(hào)；綠色：ISI；紅色：ISI+noise')
hold on
stem(1:N,y2,':r')
stem(1:N,rec_sig2,':g')
hold off